Effect of endogenous prostaglandin synthesis on the response of the umbilical vasculature to norepinephrine. Using near-term chronically catherized sheep we will examine the response of the umbilical vasculature to test infusions of norepinephrine. We will measure the blood flows using radioactive microspheres before and after norepinephrine. The resistance of the umbilical circulation will be defined as blood flow divided by arterial minus pressure. The arterial pressure will be the pressure measured in the hindlimb artery and the venous pressure will be the pressure measured in a placental vein. We will repeat this experiment after pretreating the fetus with indomethacin and compare the change in resistance to norepinephrine in the normal fetus with that observed after the blockade of endogenous prostaglandin synthesis. In a separate series of experiments we will use meclofenamate to inhibit prostaglandin synthesis to ensure that the results that we are observing are indeed due to the inhibition of prostaglandin synthesis rather than due to some side effect of the drug used. Using the same preparation we will examine the response of the maternal placental vasculature to varying doses of indomethacin. It is postulated that if endogenous prostaglandins play a role in the regulation of the flow to this vasuclar bed then will see this effect indirectly by blocking the synthesis of prostaglandins with exogenous indomethacin. It is expected that the results of these experiments will be relevant to our understanding of the factors regulating the blood flows to the near-term placenta and assist in our understanding of the etiology of disease such as preeclampsia.